SHANGHAI, May 8 (Reuters) - China stocks rebounded on Friday, stemming a three-day sell-off that led a key share index to its worst weekly decline in nearly five years amid fears of regulatory crackdown on speculators.

The Shanghai Composite Index rose 2.3 percent, to 4,205.92 points. But for the week, the index fell 5.3 percent, posting its worst performance since July 2010.

The CSI300 index climbed 2.0 percent, to 4,558.40, but posted a weekly decline of 4 percent, the biggest in one and a half years.

The poor performance was triggered by signs of tighter regulatory scrutiny over margin lending, which has helped fuel a near doubling in China's stock market over the past year despite a flagging economy.

Data on Friday showed that China's exports unexpectedly fell 6.4 percent in April from a year earlier, while imports tumbled by a deeper-than-forecast 16.2 percent.

The poor trade figures reinforced expectations of that Beijing will deliver fresh stimulus, and were interpreted as being good news to the stock market, according to Gerry Alfonso, director of Shenwan Hongyuan Securities Co.

He said Friday's improvement in sentiment was also "likely caused by investors seeing opportunities after three days of corrections."

Even after this week's sharp pull-back, China's stock market is still up nearly 30 percent so far this year, the best performer in Asia, and easily outpacing major U.S. and European indexes.

Short-term volatility doesn't put an end to China's bull run, which "still has a long way to go," said Fang Weiling, fund manager of Bosera Asset Management. "The stock market is tasked with propelling reform and promoting innovation."

The government wants the market to rise at a slower, more sustainable pace, rather than risking a sharp and unruly run-up that could end in a sudden destabilising crash, according to Qi Yifeng, analyst at CEMB Group Ltd.

"Investors are very clever," he said. "As soon as they got the signal that regulators don't want main indexes to rise too quickly, they dump index-heavyweights but continue to play small-cap stocks."

Shenzhen's start-up board ChiNext surged 6 percent on Friday to record highs, notching its biggest one-day rise in four and a half years.

Technology related stocks also jumped, after the government vowed to vigorously promote e-commerce and expedite funding by Internet companies.

But banking shares rose slightly, with some analysts attributing the underperformance to rising bad debts in the first quarter. Real estate shares also lagged the rise in the broader market.

Despite their lofty valuations, tech stocks have a bright future because they are key to China's economic restructuring, said Zhang Yunyi, general manager of Shanghai Hongyi Investment & Management Co., who expected the gap between their prices and fundamentals to be filled over time. (Editing by Simon Cameron-Moore)